Stack molding provides an advantage over single molding in that it enables the output of an injection molding machine to be at least doubled without significantly increasing its size. Stack mold configurations generally employ a stationary first platen, a movable center platen and a movable second platen. The mold cavities are conventionally located on opposing faces of the movable center platen. The movable center platen and the second movable platen reciprocate to open and close the mold cavities during a production cycle. In a stack molding apparatus, the melt runner system or the manifold system extends through the center platen in order to reach the mold cavities located on each side of the center platen via an equal path length.
Typically, multi-cavity stack molds use a pair of melt transfer nozzles to provide a direct melt channel between the extruder nozzle of the injection molding machine and its hot runner distributor, or manifold, which is mounted in the center platen of the stack mold. The manifold delivers melt to injection nozzles that are associated with the mold cavities.
As a result of the reciprocating action of the movable platens, the melt transfer nozzles are continuously coupled to, and decoupled from, one another. This often causes drooling and/or stringing of the melt to occur, which is undesirable.
A need therefore exists for a melt transfer device that controls the flow of the pressurized melt stream such that when the melt transfer nozzles are decoupled from one another the occurrence of drooling and/or stringing is reduced.